The proposed research will evaluate the effectiveness of the opiate antagonist naltrexone and positive behavioral intervention programs in treating self-injurious behavior in 24 adults with developmental disabilities in community residential settings. Several converging lines of evidence suggest that self-injurious behavior is a multiply determined phenomenon with several distinct etiologies and/or current regulatory mechanisms. While many forms of self-injury appear to be maintained by environmental consequences (e.g., attention from others, escape from unpleasant or demanding tasks, access to preferred objects or activities), others appear to have a neurochemical basis. Recent research reveals that some forms of self-injury are responsive to treatment with opiate antagonist drugs, suggesting the involvement of the endorphin/enkephalin ligand system in the maintenance of self-injurious behavior. In addition to attenuating pain, endorphins serve as powerful reinforcing stimuli. It is proposed that after repeated self-injury, with associated endorphin release, an individual becomes physically dependent upon the endogenous opioid chemicals. Because discontinuation of self-injury would induce an opiate-type abstinence syndrome, the individual may continue to engage in self-injury to avoid withdrawal distress. Our preliminary work on this topic, together with the results of several published reports, implicate opioid mechanisms in self-injury in people with developmental disabilities. In a majority of cases, treatment with opiate antagonist drugs reduce or eliminate self-injury. However, some patterns of self-injury are not responsive to opiate antagonists, suggesting the involvement of other factors. Recent evidence indicates that patterns of self-injury can be distinguished on the basis of the environmental circumstances under which it occurs, which may provide a basis for isolating distinct subgroups of self-injurious individuals. The goal of the proposed research is to integrate these environment-based approaches with those based on opioid mechanisms in the treatment of self-injurious behavior. A two-phase experimental/treatment strategy is proposed, wherein two groups of 12 subjects each will receive either naltrexone or behavioral interventions during one phase and a combination of both treatments during a second phase. The naltrexone trial will consist of a double-blind crossover design with placebo and 100 mg/day naltrexone. The behavioral interventions will focus on replacing self-injurious behavior with functional, adaptive skills. Frequency and intensity of self-injury constitute primary dependent variables, as measured by direct observational methods and by staff ratings. In addition, the present research will include a detailed microanalysis of the ongoing environmental circumstances accompanying both self-injury and other response classes that covary with self-injury. This will not permit greater specification of the environmental mechanisms through which self-injury occurs under normal (pre-intervention) conditions, it will also reveal how the ongoing stream of behavior, including adaptive functioning, is modified by naltrexone, by behavioral interventions, and by their combination.